1. Field of the Invention
The invention relates to a system for displaying images, and more particularly to a system for displaying images which includes a full-color organic electroluminescent device.
2. Description of the Related Art
Recently, with the development and wide application of electronic products, such as mobile phones, and notebook computers, there has been increasing demand for flat display elements which consume less power and occupy less space. Organic electroluminescent elements are popular for use in flat panel displays as they are self-emitting and highly luminous, provide wide viewing angles, have a fast response speed, and a simple fabrication process.
An organic light-emitting diode (OLED) is a light-emitting diode that uses an organic electroluminescent layer and is being employed more and more in flat panel displays. One trend in organic electroluminescent display technology is for achieving higher luminescent efficiency and a longer operating life span. To further improve the performance of OLEDs and achieve a full-color image, a new kind of OLED structure called tandem OLED (or stacked OLED, or cascaded OLED) has been developed,
U.S. Pat. No. 5,703,436 discloses a stacked full-color organic electroluminescent device fabricated by vertically stacking individual red, blue, and green OLEDs and driven by a single power source. The stacked full-color organic electroluminescent device requires a high driving voltage, and the emission color thereof varies with differences in the applied current.
U.S. Pat. No. 7,193,361 discloses a full-color organic electroluminescent device which reduces a driving voltage thereof, and includes an anode and a cathode. A plurality of emitting layers is disposed between the anode and the cathode, and hole transport layers are directly disposed on a surface thereof, which faces toward the anode of each emitting layer, respectively. The voltage of the full-color organic electroluminescent device is reduced in comparison with the conventional full-color organic electroluminescent device, but the NTSC ratio of the full-color organic electroluminescent device is less than desired and a significant problem.